Certain Starch May Reduce Colon-Cancer Risk of Meat-Heavy Diet

By Bahar Gholipour, Staff Writer | August 04, 2014 12:15am ET

Eating your steak with a side of potatoes and beans may be one way to reduce the colon cancer risk that comes with eating red meat — findings from a new study suggests the "resistant" starch, found in root vegetables, grains and legumes, may reverse some of the damaging effects of red meat on cells.

Researchers looked at23 healthy study participants who were randomly assigned to eat either about 0.6 lbs. (300 grams) of red meat per day for four weeks, or the same diet with the addition of 0.1 lbs. (40 grams) of resistant starch per day. Resistant starches are carbohydrates that go undigested in the small intestine, and later get fermented by bacteria in the colon. After a break, the participants switched diets, so everyone spent four weeks on each diet during the study.

The researchers found that eating the diet high in red meat changed levels of a type of genetic material called microRNA in rectal tissue. Specifically, the scientists found an increase in certain microRNAs linked to colon cancer. [Cancer-Fighting Diet: 6 Tips to Reduce Your Risk]

However, adding resistance starch to the diet mitigated some of this increase, according to a study published today (Aug. 4) in the journal Cancer Prevention Research.

"Red meat and resistant starch have opposite effects on the colorectal cancer-promoting microRNAs," study author Karen Humphreys, a researcher at Flinders University in Adelaide, Australia, said in a statement. "This finding supports consumption of resistant starch as a means of reducing the risk associated with a high red-meat diet."

Colon cancer develops in the cells lining the inside of the colon and rectum, often beginning as a polyp, but then growing into a cancerous tumor. Consuming too much alcohol, smoking and not exercising are among risk factors for colon cancer.

Studies have found that people who eat a lot of red meat are more likely to develop colon cancer, whereas those who eat a lot of fiber appear to have a reduced risk of the cancer.

Further research is needed to determine whether a diet high in resistant starch results in a lower risk of actually developing cancer. But there is reason to think that eating resistant starch does bring such a benefit. When it is broken down, starch transforms into compounds called butyrates, which are important for cells' metabolism. Lab studies have found butyrates affect colon cancer cells by altering their microRNAs, which in turn regulate gene expression.

The researchers noted that the amount of red meat people ate during the study may exceed levels consumed by many people in the general population, but the amount of resistant starch used in the study was realistic. For the study, the researchers used a supplement of starch, but resistant starch can be found in many natural foods.

"Good examples of natural sources of resistant starch include bananas that are still slightly green, cooked and cooled potatoes [such as those in potato salad], whole grains, beans, chickpeas, and lentils. Scientists have also been working to modify grains such as maize so they contain higher levels of resistant starch," Humphreys said.

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Bahar Gholipour

Bahar Gholipour is a staff reporter for Live Science covering neuroscience, odd medical cases and all things health. She holds a Master of Science degree in neuroscience from the École Normale Supérieure (ENS) in Paris, and has done graduate-level work in science journalism at the State University of New York at Stony Brook. She has worked as a research assistant at the Laboratoire de Neurosciences Cognitives at ENS.